derive public to public child keys

CHANGELOG.md

@@ -1,6 +1,7 @@
 0.2.0 / 2014-06-25
 ------------------
 - upgraded `"ecurve": "^0.8.0"` to `"ecurve": "^1.0.0"`
+- added functionality to dervice public to public child keys
 
 0.1.0 / 2014-06-16
 ------------------

lib/hdkey.js

@@ -2,7 +2,7 @@ var assert = require('assert')
 var crypto = require('crypto')
 var BigInteger = require('bigi')
 var ecurve = require('ecurve')
-var ecparams = ecurve.getCurveByName('secp256k1')
+var curve = ecurve.getCurveByName('secp256k1')
 var Point = ecurve.Point
 var sha512 = require('sha512')
 
@@ -39,7 +39,8 @@ Object.defineProperty(HDKey.prototype, 'privateKey', {
     assert.equal(value.length, 32, 'Private key must be 32 bytes.')
     this._privateKey = value
     this._privateKeyInteger = BigInteger.fromBuffer(this._privateKey)
-    this._publicKey = ecparams.G.multiply(this._privateKeyInteger).getEncoded(true) //force compressed point
+    this._publicPoint = curve.G.multiply(this._privateKeyInteger)
+    this._publicKey = this._publicPoint.getEncoded(true) //force compressed point
     this._identifier = hash160(this.publicKey)
     this._fingerprint = this._identifier.slice(0, 4).readUInt32BE(0)
   }
@@ -51,8 +52,8 @@ Object.defineProperty(HDKey.prototype, 'publicKey', {
   },
   set: function(value) {
     assert(value.length === 33 || value.length === 65, 'Public key must be 33 or 65 bytes.')
-    var pt = Point.decodeFrom(ecparams, value)
-    this._publicKey = pt.getEncoded(true) //force compressed point
+    this._publicPoint = Point.decodeFrom(curve, value)
+    this._publicKey = this._publicPoint.getEncoded(true) //force compressed point
     this._identifier = hash160(this.publicKey)
     this._fingerprint = this._identifier.slice(0, 4).readUInt32BE(0)
     this._privateKey = null
@@ -128,10 +129,10 @@ HDKey.prototype.deriveChild = function(index) {
   // Private parent key -> private child key
   if (this.privateKey) {
     // ki = parse256(IL) + kpar (mod n)
-    var ki = pIL.add(BigInteger.fromBuffer(this.privateKey)).mod(ecparams.n)
+    var ki = pIL.add(BigInteger.fromBuffer(this.privateKey)).mod(curve.n)
 
     // In case parse256(IL) >= n or ki == 0, one should proceed with the next value for i
-    if (pIL.compareTo(ecparams.n) >= 0 || ki.signum() === 0) {
+    if (pIL.compareTo(curve.n) >= 0 || ki.signum() === 0) {
       return this.derive(index + 1)
     }
 
@@ -141,14 +142,16 @@ HDKey.prototype.deriveChild = function(index) {
   } else {
     // Ki = point(parse256(IL)) + Kpar
     //    = G*IL + Kpar
-    //var Ki = ecparams.getG().multiply(pIL).add(this.pub.Q)
+    var Ki = curve.G.multiply(pIL).add(this._publicPoint)
 
     // In case parse256(IL) >= n or Ki is the point at infinity, one should proceed with the next value for i
-    //if (pIL.compareTo(ecparams.getN()) >= 0 || Ki.isInfinity()) {
-    //  return this.derive(index + 1)
-    //}
+    if (curve.isInfinity(Ki)) {
+      return this.derive(index + 1)
+    }
 
     //hd.pub = new ECPubKey(Ki, true)
+    //this._publicPoint = Ki
+    hd.publicKey = Ki.getEncoded(true)
   }
 
   hd.chainCode = IR

test/hdkey.test.js

@@ -4,7 +4,7 @@ var BigInteger = require('bigi')
 var cs = require('coinstring')
 var ecurve = require('ecurve')
 var secureRandom = require('secure-random')
-var ecparams = ecurve.getCurveByName('secp256k1')
+var curve = ecurve.getCurveByName('secp256k1')
 
 var HDKey = require('../')
 var fixtures = require('./fixtures/hdkey')
@@ -46,7 +46,7 @@ describe('hdkey', function() {
 
     it('should not throw if key is 33 bytes (compressed)', function() {
       var priv = secureRandom.randomBuffer(32)
-      var pub = ecparams.G.multiply(BigInteger.fromBuffer(priv)).getEncoded(true)
+      var pub = curve.G.multiply(BigInteger.fromBuffer(priv)).getEncoded(true)
       assert.equal(pub.length, 33)
       var hdkey = new HDKey()
       hdkey.publicKey = pub
@@ -54,7 +54,7 @@ describe('hdkey', function() {
 
     it('should not throw if key is 65 bytes (not compressed)', function() {
       var priv = secureRandom.randomBuffer(32)
-      var pub = ecparams.G.multiply(BigInteger.fromBuffer(priv)).getEncoded(false)
+      var pub = curve.G.multiply(BigInteger.fromBuffer(priv)).getEncoded(false)
       assert.equal(pub.length, 65)
       var hdkey = new HDKey()
       hdkey.publicKey = pub
@@ -66,7 +66,7 @@ describe('hdkey', function() {
       it('should parse it', function() {
         //m/0/2147483647'/1/2147483646'/2
         var key = "xprvA2nrNbFZABcdryreWet9Ea4LvTJcGsqrMzxHx98MMrotbir7yrKCEXw7nadnHM8Dq38EGfSh6dqA9QWTyefMLEcBYJUuekgW4BYPJcr9E7j"
-        var keyBuffer = cs.decode(key).slice(0, 78)//bs58.decode(key).slice(0, 78)
+        var keyBuffer = cs.decode(key)
         var hdkey = HDKey.fromExtendedKey(keyBuffer)
         assert.equal(hdkey.versions.private, 0x0488ade4)
         assert.equal(hdkey.versions.public, 0x0488b21e)
@@ -84,7 +84,7 @@ describe('hdkey', function() {
       it('should parse it', function() {
         //m/0/2147483647'/1/2147483646'/2
         var key = "xpub6FnCn6nSzZAw5Tw7cgR9bi15UV96gLZhjDstkXXxvCLsUXBGXPdSnLFbdpq8p9HmGsApME5hQTZ3emM2rnY5agb9rXpVGyy3bdW6EEgAtqt"
-        var keyBuffer = cs.decode(key).slice(0, 78)//bs58.decode(key).slice(0, 78)
+        var keyBuffer = cs.decode(key)
         var hdkey = HDKey.fromExtendedKey(keyBuffer)
         assert.equal(hdkey.versions.private, 0x0488ade4)
         assert.equal(hdkey.versions.public, 0x0488b21e)
@@ -98,4 +98,19 @@ describe('hdkey', function() {
       })
     })
   })
+
+  describe('> when deriving public key', function() {
+    it('should work', function() {
+      var key = "xpub661MyMwAqRbcFtXgS5sYJABqqG9YLmC4Q1Rdap9gSE8NqtwybGhePY2gZ29ESFjqJoCu1Rupje8YtGqsefD265TMg7usUDFdp6W1EGMcet8"
+      var keyBuffer = cs.decode(key)
+      var hdkey = HDKey.fromExtendedKey(keyBuffer)
+
+      var path = "m/3353535/2223/0/99424/4/33"
+      var derivedHDKey = hdkey.derive(path)
+
+      var expected = "xpub6JdKdVJtdx6sC3nh87pDvnGhotXuU5Kz6Qy7Piy84vUAwWSYShsUGULE8u6gCivTHgz7cCKJHiXaaMeieB4YnoFVAsNgHHKXJ2mN6jCMbH1"
+      assert.equal(cs.encode(derivedHDKey.publicExtendedKey), expected)
+
+    })
+  })
 })